The present invention relates to barrier movement operators and particularly to barrier movement operators having improved characteristics for detecting obstructions to the movement of the barrier.
Barrier movement operators generally comprise an electric motor coupled to a barrier and a controller which responds to user input signals to selectively energize the motor to move the barrier. The controller may also respond to additional input signals, such as those from photo-optic sensors sensing an opening over which the barrier moves, to control motor energization. For example, should a photo optic sensor detect an obstruction present in the barrier opening, the controller may respond by stopping and/or reversing motor energization to stop and/or reverse barrier movement. The controller may also respond to motor speed representing signals by controlling motor energization. Such may be used to stop and/or reverse the movement of a barrier when the motor speed, which represents the speed of movement of the barrier, falls below a predetermined amount as might occur if the barrier has contacted an obstruction to its movement.
Detecting contact by the barrier with an obstacle by sensing the driving speed of the motor has certain inherent difficulties. The barrier, barrier guide system and the connection between the barrier and the motor all have momentum and all exhibit some amount of flexibility. When the leading edge of a barrier is slowed, it takes time for the inertia of the various parts to be overcome and for the slowing of the barrier to be reflected back to the motor via the flexible (springy) interconnection. Through proper design and construction techniques, such systems have been successfully achieved for response times and contact pressure thresholds to achieve safe operation. However, to achieve ever safer operation involving lower barrier contact forces and more rapid response times, new designs are needed.
Motors for use with barrier movement operators are generally constructed or selected to operate efficiently and exhibit a motor rotation rate (motor speed) to torque characteristic represented in FIG. 4. The normal forces on the barrier generally allow the operating motor speed between the marks labeled A and B on FIG. 4 resulting in a relatively flat slope of the speed versus torque characteristic. The “normal” motor having a characteristic as shown in FIG. 4 exhibits a change of motor RPM of approximately 20 RPM per inch-pound of required motor torque. Improvements in obstruction contact times and reduction of obstruction contact forces is difficult with a motor having the characteristics of FIG. 4 because the change of motor RPM is small for the normal range of obstruction forces. A need exists for a motor which operates with a torque to speed characteristic which is enhanced for rapid obstacle detection.
Improvements in barrier contact obstacle detection may also be achieved by improvements in how sensed motor speed changes are interpreted. Existing barrier movement systems include obstacle detection functions which compare currently measured motor speed with an obstacle indicating threshold. The obstacle indicating threshold generally consists of an expected motor speed minus a constant which defines how much additional speed reduction represents an obstacle rather than a normal variation in operating speed. In some systems an average speed is assumed for the entire movement between open and closed positions and when motor speed falls below the normal speed minus a fixed threshold an obstacle is assumed. In other systems a speed history is determined for door movement by recording measured speeds at several (many) points along barrier travel. When the measured speed falls below the speed history for the same point in barrier travel minus a fixed threshold, an obstacle is assumed. Improvements are needed in obstacle detection to permit fine control of speed changes which indicate an obstruction.